I have the same VAIO model and experienced the same problem once I formated system full of crappy trialware trash apps and installed clean Windows 7.
Solution is to use graphic drivers
from Sony support webpage. They probably made some stupid modifications to drivers, so standard Intel drivers don't work and we are all doomed to use drivers from Sony only. :-(
Otherwise this notebook isn't bad. I got it new for 500€ one week ago.